System and Method for Selective Communication with RFID Transponders

ABSTRACT

A system having an RFID transceiver is adapted to communicate exclusively with a single RFID transponder located in a predetermined confined transponder target area. The system includes a magnetic coupling device comprising a magnetic flux generator responsive to a radio frequency input signal and a magnetic field pattern former. The pattern former is configured to collect flux produced by the flux generator and to form a field pattern in the location of the transponder target area. The system establishes, at predetermined transceiver power levels, a mutual magnetic coupling which is selective exclusively for a single transponder located in the transponder target area.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to RFID communication systems which are selectivefor an individual transponder located in a predetermined target area, tothe exclusion of other transponders, and to printers and other largersystems having such RFID communication systems.

2. Description of Related Art

Inductively coupled radio frequency identification (RFID) technologyallows data acquisition and or transmission from and or to active(battery powered) or passive RFID transponders using RF magneticinduction. To read or write from and or to an RFID transponder, the RFIDtransponder is exposed to an RF magnetic field that couples with andenergizes the RFID transponder through magnetic induction and transferscommands and data using a predefined “air interface” RF signalingprotocol.

When multiple RFID transponders are within the range of the same RFmagnetic field they will each be energized and attempt to communicatewith the transceiver, potentially causing errors in reading and orwriting to a specific RFID transponder. Anti-collision managementtechnologies exist to allow near simultaneous reading and writing tonumerous RFIDs in a common RF magnetic field. However, anti-collisionmanagement increases system complexity and cost. Further, anti-collisionmanagement is blind. It cannot recognize where a responding transponderis located in the RF magnetic field.

One way to prevent errors during reading and writing to RFIDtransponders without using anti-collision management is to isolate eachRFID transponder from nearby RFID transponders. Previously, isolation ofRFID transponders has used RF shielded housings and or anechoic chambersthrough which the RFID transponders are individually passed for isolatedexposure to the interrogating RF magnetic field. This requires that theindividual transponders have cumbersome shielding or a significantphysical separation.

When RFID transponders are supplied attached to a carrier substrate, forexample in RFID-mounted labels, tickets, tags or other media supplied inbulk rolls, Z-folded stacks or other format, an extra portion of thecarrier substrate is required to allow one RFID transponder on thecarrier substrate to exit the isolated field area before the next RFIDtransponder in line enters it. The extra carrier substrate increasesmaterials costs and the required volume of the RFID media bulk supplyfor a given number of RFID transponders. Having increased spacingbetween RFID transponders may also slow overall throughput.

When the size or form factor of the utilized RFID transponder ischanged, the RF shielding and or anechoic chamber configuration may alsorequire reconfiguration, adding cost and complexity and reducing overallproductivity.

There exists applications wherein it is desired to print ontransponder-mounting media in the same target space in which thetransponder is being read from or written to. This may be very difficultto accomplish if the transponder must be interrogated in a shieldedhousing or chamber.

Printers have been developed which are capable of on-demand printing onlabels, tickets, tags, cards or other media with which is associated anRFID transponder. These printers have an RFID transceiver for on-demandcommunicating with the RFID transponder on the individual media. For thereasons given, it is highly desirable in many applications to presentthe media on rolls or other format in which the transponders are closelyspaced. However, close spacing of the transducers exacerbates the taskof serially communicating with each individual transponder withoutconcurrently communicating with transponders on neighboring media. Thisselective communication exclusively with individual transponders isfurther exacerbated in printers designed to print on the media in thesame space as the transponder is positioned when being interrogated.

Competition in the market for such “integrated” printer-transceiversystems and selective RFID interrogation systems has focused attentionon minimization of overall costs, including reduction of the costs ofindividual RFID transponders, bulk RFID label and or tag supply carriersubstrates, printers and or interrogators.

Therefore, it is an object of the invention to provide a system andmethod which overcomes deficiencies in such prior art.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a side schematic view of a media printer according to oneembodiment of the invention having an improved RFID interrogationsystem.

FIG. 2 is a top view of a magnetic coupling device embodying principlesof the present invention.

FIG. 3 is a bottom view of the magnetic coupling device of FIG. 2.

FIG. 4 is a top view of the magnetic coupling device of FIG. 2, with amagnetic field pattern former applied.

FIG. 5 is a bottom view of the magnetic coupling device of FIG. 4.

FIG. 6A is a cut-away side view of a magnetic coupling device as shownin FIGS. 4 and 5, illustrating schematically a mutual magnetic couplingselectively with a single RFID transponder supplied in-line with otherRFID transponders on a carrier substrate.

FIG. 6B is a view similar to FIG. 6A of an alternative embodiment of anaspect of the invention.

FIG. 7 is a partial cut-away top schematic view of the magnetic couplingdevice and carrier substrate mounted RFID transponders of FIG. 6A; aprinthead and platen roller have been omitted for clarity.

FIG. 8A is a test chart showing relative power levels delivered foractivation by a magnetic coupling device of the invention of severaldifferent types of RFID transponders, in “landscape” orientation, as afunction of location of the transponder along a feed path of ahypothetical media printer.

FIG. 8B is a test chart similar to that of FIG. 8A but with thetransponders in a “portrait” orientation.

FIG. 9 is a test chart showing successful RFID transponder writes withrespect to the position of an RFID transponder along a feed path of alabel printer containing a magnetic coupling device according to oneembodiment of the invention having a constant magnetic coupling devicepower level.

FIG. 10 is a chart showing a range of acceptable RFID transponderlocations and substrate dimensions for use with a magnetic couplingdevice according to one embodiment of the invention.

DETAILED DESCRIPTION

The present invention concerns apparatus and method which enables anRFID transceiver (sometimes termed herein an “interrogator”) tocommunicate selectively and exclusively with a single RFID transponderwhen one or more other transponders are in close proximity, without theneed for physical isolation or cumbersome shielded housings or chambers.

The invention is useful in the loading or reading of transponders, forexample on an assembly line, in distribution centers or warehouses whereon-demand RFID labeling is required, and in a variety of otherapplications. In many applications a transponder or a number oftransponders are mounted on a label, ticket, tag, card or other mediacarried on a liner or carrier. It is often desirable to be able to printon the media before, after, or during communication with a transponder.Although this invention is disclosed here in a specific embodiment foruse with a direct thermal or thermal transfer printer, it may also beused with any other type of printer using other printing technologies,including inkjet, dot-matrix, and electro-photographic methods.

In some applications a print station may be at a distance from the RFIDtransceiver; in others it may be necessary to accomplish the printfunction in the same general space occupied by the transponder when itis being interrogated (sometimes herein termed the “transponder targetarea”).

FIG. 1 illustrates by way of example only an implementation of theinvention in a thermal transfer label printer 12 in which both printingand transponder communication are accomplished, but at differentlocations in the printer.

As shown in FIG. 1, the printer 12 includes a printhead sub-assembly 15comprising a conventional thermal printhead 14 and platen roller 16, asin a direct thermal printer for printing on thermally-sensitive media. Aweb 24 of media, such as labels, tickets, tags or cards, is directedalong a feed path 26 to the printhead 14 where the printhead 14 applieson demand text and/or graphics under control of a computer ormicroprocessor (not shown). After being printed, the media may be peeledoff the underlying carrier substrate 20 at a tear bar 32 and follows amedia exit path 34. The liner or carrier substrate 20 for the media isguided out of the printer 12 by a roller 36 where it exits the printeralong an exit path 38.

When a thermal printer is configured for use as a thermal transferprinter, a ribbon supply roll 18 delivers a thermal transfer ribbon (notshown for clarity) between printhead 14 and the media on web 24. Afteruse, the spent ribbon is collected on a take-up reel 22.

In accordance with an aspect of the present invention, the printerincludes a transceiver 42 and a magnetic coupling device 1 locatedproximate the media feed path 26. As will be explained and illustratedin detail hereinafter, the system (including transceiver 42 and magneticcoupling device 1) forms a magnetic flux field pattern in the locationof a transponder target area 44 (see FIG. 6A). The system is configuredto establish at predetermined transceiver power levels a mutual magneticcoupling which is selective exclusively for a single transponder locatedin the transponder target area 44.

As labels or other media with embedded transponders move along the mediafeed path 26, through target area 44, data may be read from and orwritten to transponder 10. Information indicia then may be printed uponan external surface of the media as the media passes between the platenroller 16 and the printhead 14 by selective excitation of the heatingelements in the printhead 14, as is well known in the art. When thethermal printer 12 is configured as a direct thermal printer, theheating elements form image dots by thermochromic color change in theheat sensitive media; when the thermal printer 12 is configured as athermal transfer printer, then ink dots are formed by melting ink fromthe thermal transfer ribbon (not shown for clarity) delivered betweenprinthead 14 and the media on web 24 from supply roll 18. Patters ofprinted dots thus form the desired information indicia on the media,such as text, barcodes or graphics.

Media conveyance is well known in the art. Therefore the mediaconveyance 25 portion of the printer that drives the media withtransponders along the media feed path 26 is not described in detail.

The magnetic coupling device 1 and its manner of operation will now bedescribed with reference to FIGS. 2-7. One embodiment of the magneticcoupling device 1 is configured for use, for example, with 13.56 MHzRFID transponders 10. Transponders 10 are bulk supplied on a carriersubstrate 20 in label, ticket, card or tag form with a printablefacestock 30.

The magnetic coupling device 1 comprises a magnetic flux generator and amagnetic field pattern former, as will be described. The magnetic fluxgenerator may comprise one or more coils responsive to RF signalssupplied by the transceiver 42. The coils may take the form of a planarelongated coil created, for example, by conductor(s) coupled with a coilsupport structure. The conductors and coil support structure maycomprise, for example, a coil trace(s) 50 on and or within amulti-layered printed circuit board (PCB) 60. Coil trace(s) 50 may beformed without sharp corners to minimize creation of impedancediscontinuities.

Because the wavelength at 13.56 MHz is approximately 22 meters, designof a small, low-cost antenna for coupling to an RFID transponder usingelectromagnetic radiation is difficult. Therefore, the magnetic couplingdevice 1 is configured to mutually couple to RFID transponder(s)operating at frequencies with long wavelengths using only magneticinduction coupling. As will be described hereinafter, electric fieldsemitted by coil trace 50 are suppressed by a grounded E-field suppressorshield 90.

The dimensions of the magnetic coupling device 1 and the number ofturns, for example three to five turns, used in the coil(s) aredetermined in part by the intended range from and longitudinaldimensions of the RFID transponder 10 which the magnetic field of themagnetic coupling device will selectively mutually inductively couplewith. Capacitors 80, for example surface mounted to the PCB 60 local tothe coils trace(s) 50, may be used for impedance matching (for example,50 ohm) and tuning of the magnetic coupling device 1, to zero theimaginary component of impedance at a desired resonant frequency. Otherimpedance matching and or magnetic coupling device tuning componentsthat may be applied include matching transformers, inductors and a tapof the magnetic coupling device coil. one or more resistor(s) 85 may beused to adjust a Q-factor of the magnetic coupling device.

The E-field suppressor shield 90 may be created, for example, by forminganother conductive layer on one or both sides of the PCB 60 containingcoil trace 50, as shown in FIGS. 2, 3, 4 and 6A and 6B. The E-fieldsuppressor shield 90 may be formed as a gapped loop that covers themagnetic coupling device radiating coil trace(s) 50 completely with theexception of a small open circuit 100, as shown in FIGS. 1 and 2. Thepurpose of the open circuit 100 is to prevent Eddy current flow in theE-field suppressor shield 90 which would cause signal losses.

Without more, the coil trace(s) of the magnetic coupling device 1 may beexpected to emit magnetic flux lines in a generally omnidirectionaltoroid pattern about the coil trace(s) 50. A transponder-selectivemagnetic field pattern former 110 is provided to collect flux producedby the flux generator (coil trace(s) 50 in the illustrated embodiment)and to form a field pattern 70 in the location of a predeterminedtransponder target area 44.

FIG. 6A illustrates an arrangement wherein a transceiver 42 and magneticcoupling device 1 are located in a printer having a printhead 14 andassociated platen roller 16 which are located proximate the transpondertarget area 44. With the printhead 14 within or near the transpondertarget area 44, a label or other media carrying a transponder can beinterrogated (read and or write) and the carrying media can be printedin essentially the same space. This is important in on demand systems,particularly portable or compact systems, where it would be impracticalto have a print station located remotely from the transponderinterrogation station.

The field pattern former 110 increases the amount of magnetic flux byinserting into the field space a material of higher magnetic fluxpermeability than free space. The field pattern former 110 has a gap 112within and adjacent to which the field pattern is formed. The gap 112 isdefined as areas of the magnetic coupling device 1, and in the presentembodiment particularly coverage of the coil trace 50, which are notcovered by the field pattern former 110. The resulting field pattern istherefore positioned and influenced by the configuration and position ofthe gap 112. In the FIG. 6A embodiment, the gap 112 may be, for example,approximately the width of one side of the coil traces 50 or may beabout 50% of the top surface area of the PCB 60 (if the coil trace 50 iscentered on the PCB 60) and is located at the end of the magneticcoupling device 1 nearest the printhead 14. Configurations that covermore or less of the coil traces 50 and or, for example, all edges of thePCB 50 are also usable to create a magnetic field pattern 70 thatmatches a desired transponder target area 44. A top view of thearrangement shown in FIG. 6A is illustrated in FIG. 7.

Alternatively, a simplified RFID transponder read and or write systemmay be formed without printing capabilities by positioning a magneticcoupling device 1 coupled to a transceiver 42 proximate a mediaconveyance moving sequential RFID transponders through a target area 44of the magnetic coupling device 1.

Such an alternative embodiment is shown in FIG. 6B wherein the gap 112in coverage by a field pattern former 110 is disposed intermediate theends of magnetic coupling device 1. The FIG. 6B embodiment is configuredfor applications wherein an associated printing function in the samephysical space is not necessary. The FIG. 6B embodiment contemplatesthat any printing or other function to be performed is accomplished atanother station. The printer 12 illustrated in FIG. 1 and describedabove is an example of an execution of the invention wherein theinterrogation of the transponders is accomplished at a distance from theprinthead 14.

The field pattern former 110 may be formed using a material preferablyhaving a magnetic relative permeability of 20 or more. The material maybe, for example, a ferrite composition. Ferrite is a general name for aclass of materials having a powdered, compressed, and sintered magneticmaterial having high resistivity, consisting chiefly of ferric oxidecombined with one or more other metals. The high resistance of ferritecompositions makes eddy-current losses extremely low at highfrequencies. Examples of ferrite compositions include nickel ferrite,nickel-cobalt ferrite, manganese-magnesium ferrite and yttrium-iongarnet. The field pattern former 110 may be a rubberized flexibleferrite, ferrite polymer film or stennite material. Flex Suppressor(trademark) material available from Tokin EMC is also a suitablematerial. The selected field pattern former 110 may be connected to thePCB 60, for example, with an adhesive. Alternatively, the field patternformer 110 may be applied in a liquid or semi liquid form, upon thedesired areas of the PCB 60 or other coil support structure andsolidified and or cured to leave, for example, only a desired gap 112uncovered by the material comprising the field pattern former 110.

The embodiment shown in FIGS. 4-7 may have a field pattern former 110 offlexible ferrite. For example, for the embodiment shown in FIGS. 4, 5,6A and 7, the field pattern former 110 covers the magnetic couplingdevice 1 area of the bottom side of the PCB 60 and extends, wrappedabout the PCB 60 in a single portion to cover approximately one half ofthe top side of the coil traces 50, resulting in the concentration offlux and the formation of a magnetic field pattern 70 within andadjacent the gap 112.

In accordance with an aspect of the present invention, the system isconfigured to establish at predetermined transceiver power levels amutual magnetic coupling which is selective exclusively for a singletransponder located in the predetermined transponder target area 44. Aswill become evident from the description of FIGS. 8A and 8B, the mutualcoupling will vary depending upon the mechanical and electricalcharacteristics of the coupled transponder, the applied power levels ofthe transceiver 42, the size and other properties of any media 20 whichsupports the transponder, the characteristics of the pattern former, andother factors.

Obviously, at some exaggerated transceiver power level transpondersoutside the transponder target area 44 may be excited. However, by thisinvention, at power levels in the range of normal transceiveroperations, and, for example, allowing for a 3 dB or greater tolerancemargin, the mutual coupling created will be highly selective for thetransponder 10 in the transponder target area 44.

The compact size of the magnetic coupling device 1 and the lack of anyother shielding requirements allows the economical addition ofsequentially spaced multiple RFID transponder format read and or writecapability to a range of sequential RFID transponder transport devices,for example label printers, to form a selective transpondercommunication module.

Because the magnetic coupling device 1 may be configured to be selectiveexclusively for a single transponder located in the transponder targetarea 44, it is now possible by this invention to use a web of mediahaving transponders which are closely spaced on the web, as shown in thefigures of this application. Prior to this invention it was extremelydifficult to communicate with just one transponder in a closely spacedseries of transponders without simultaneously activating adjacenttransponders.

FIGS. 8A and 8B are test charts showing relative power levels deliveredfor activation by a magnetic coupling device according to the inventionof several different types of rectangular transponders as a function oflocation along the feed path 26 of printer 12, and the orientation ofthese transponders along the web 24. FIG. 8A shows data for selectedtransponders in the “landscape” orientation similar to FIG. 7. FIG. 8Bshows data for selected transponders in the “portrait” orientation, inwhich the long axis of the transponder is along feed path 26. The FIGS.8A and 8B charts reveal how highly sensitive the system of the inventionis for a transponder located in the transponder target area 44, and howhighly non-sensitive the system is for any transponder outside thetarget area 44.

The different curves in the FIGS. 8A and 8B charts are associated withdifferent commercially available 13.56 MHz RFID transponders, aslabeled. Here, the RFID integrated types, antenna geometries and/ormanufacturers of the selected transponders are not in themselvesimportant, as they are used only as examples to demonstrate the effectof the invention. The curves themselves reflect how the mutual couplingwith the various selected transponders results in different positionsensitivity to excitation within the transponder target area 44.

The different curves shown in the charts of FIGS. 8A and 8B are notmagnetic field distributions, but rather estimates of the availablepower margin over the reading threshold for each type of transponder asa function of orientation and position relative the target area 44. Thismeasurement is made by applying a constant-power RF signal to themagnetic coupling device 1 through a variable RF attenuator; thenincreasing the attenuation in decibels until the reading of data fromtransponder 10 stops; and finally recording the attenuation value as afunction of position and orientation on the appropriate chart in FIG. 8Aor 8B. These charts are used to select an optimal location within thelabels, tickets, tags or cards for embedding the transponders, anddetermine the minimum allowable spacing between transponders along theweb 24.

To better understand the FIGS. 8A and 8B charts, an explanation withrespect to one of the curves, identified as describing thecharacteristics of a “Lintec I*CODE 16×47 mm” RFID transponder, will bemade in detail. In the example shown in FIG. 8A, the curve begins at afirst position where the front edge of the coil of the transponder 10 islocated in the target area 44 at a distance of 16 mm from a reference“0” line defined by the sharp corner edge of the tear bar 32. At thispoint, the leading edge of the transponder 10 antenna coil is alsolocated 2 mm back of a second reference line labeled “print line” ofprinthead 14. The print line is analogous to the print line in FIG. 6Awhere the printhead 14 engages a media to be printed. The Lintec I*CODE16×47 mm transponder curve shows that, at the designated transceivertest power level, the transponder cannot be activated.

In this printer configuration, moving the transponder back only 2 mm toa position 18 mm from the reference “0” line and 4 mm behind the “printline”, the transponder is responsive until the test transceiver powerlevel is suppressed 6 dB. If the transponder is moved back another 4 mm,to a position 8 mm behind the “print line” the transceiver test powerlevel must be attenuated a full 13 dB before the transponder will notrespond normally.

The back side of the Lintec I*CODE 16×47 mm curve is equally steep. Withthe transponder moved back only 14 mm from the print line; thetransponder responds normally with the test transceiver power levelsuppressed up to 12 dB. However, with the transponder moved back just 20mm from the print line, the transponder will not respond to thetransceiver delivering the test power level.

The transponder is 16 mm wide and 47 mm long. In a landscape orientationwith respect to the direction of media travel, as soon as the leadingedge of the transponder coil clears either side of a roughly 17 mmtarget area, it is unable to be activated. The other curves demonstrateresponses of a range of different RFIDs using the same testconfiguration. Allowing for the possible use of all the differenttransponders with the same magnetic coupling device configurationprovides a usable target area of 25 mm or less. With this degree ofselectivity provided by the present invention, transceiver power levelscan be raised to provide a comfortable safety margin without concern forenergizing adjacent transponders even when the transponders are closelyspaced. Conversely, the target area is wide enough that pinpointpositioning of the transducer is not necessary for reliablecommunication.

Results in the portrait orientation shown in FIG. 8B are less closelydefined. When the longer dimension of the RFID transponder is along thefeed path 26, the magnetic coupling device 1 may inductively couplealong any portion of the extended length of RFID transponder 10, even ifa majority of the transponder area is outside the target area 44.

Another way to measure the system performance is shown in FIG. 9. FIG. 9is a test chart demonstrating the number of successful write operationsout of ten attempts as a typical Phillips I*Code (trademark) 13.56 MHzRFID transponder with a 12×38 mm antenna coil is moved across the printmedia path of a Zebra Technologies, Inc. model R402 label printer/RFIDprogrammer, equipped with a magnetic coupling device 1 according to thepresent invention. The RFID transponder location for each test series isshown relative to either side of the printer's tear bar (representing“0” on the tag position axis), along the print media path. Results ofthree different test series taken with 13.56 MHz RF excitation and themagnetic coupling device 1 resonant at frequencies 13.31, 13.56, and13.81 MHz respectively are shown for each location at 1 mm increments.FIG. 9 demonstrates that the focused magnetic field pattern 70 generatedby the present invention may be configured to cause successful inductivecoupling with an RFID transponder only within a very closely definedtarget area, permitting the RFID transponders to be closely sequentiallyspaced together without causing read and or write collisions throughaccidental activation of multiple transponders.

FIG. 10 shows an RFID transponder placement map, also for I*Code 12×38mm RFID transponders, derived from testing on the model R402 similar tothat shown in FIGS. 8 and 9 for a plurality of different transponderlocations. Labels having a width “a” of at least 21 mm; a length “b” ofbetween 29 and 102 mm; a lead edge distance “y” of between 8 and 22 mm;and a label spacing “s” of a minimum of 1 mm are possible. From thisform of testing, specific to each RFID transponder, a minimumperiodicity “P” for a specific RFID transponder may be calculated asP=a+s. The value of “P” then becomes the same as the minimum RFIDtransponder spacing, leading edge to leading edge (as well as theminimum label repeat distance along the web) required to ensure thatread and or write collisions do not occur for the selected RFIDtransponder and magnetic coupling device 1 combination.

The magnetic field pattern former 110 may be easily adjusted fordifferent desired magnetic field directions and or shapes duringmanufacture by varying the size, configuration and or location of themagnetic field pattern former 110 applied to the PCB 60 or other coilsupport structure. Table of Parts  1 magnetic coupling device 10transponder 12 printer 14 printhead 15 printhead sub-assembly 16 platenroller 18 supply roll 20 carrier substrate 22 take up reel 24 web 25media conveyance 26 feed path 30 facestock 32 tear bar 34 label exitpath 36 roller 38 carrier exit path 42 transceiver 44 target area 50coil trace 60 printed circuit board 70 field pattern 80 capacitors 85resistor 90 E-field suppressor shield 100  open circuit 110  fieldpattern former 112  gap

Where in the foregoing description reference has been made to ratios,integers or components having known equivalents then such equivalentsare herein incorporated as if individually set forth.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin considerable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, representativeapparatus, methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departurefrom the spirit or scope of applicant's general inventive concept.Further, it is to be appreciated that improvements and/or modificationsmay be made thereto without departing from the scope or spirit of thepresent invention as defined by the following claims.

1. A method of establishing communication between a transceiver and asingle RFID transponder located in a predetermined confined transpondertarget area, comprising: generating a magnetic flux field which variesin response to a radio frequency input signal; and collecting andforming said magnetic field pattern in the location of said transpondertarget area; and establishing at predetermined power levels of thetransceiver a mutual magnetic coupling which is selective exclusivelyfor a single transponder located in said transponder target area.
 2. Themethod defined by claim 1 including locating in said magnetic flux fielda ferrite structure having a gap, said field pattern being formed withinand adjacent to said gap.
 3. The method defined by claim 1 includingtransporting a web of labels through said target area, at least some ofwhich labels have an RFID transponder, and wherein said method includesprinting on said labels.
 4. The method defined by claim 1 includingsuppressing electric fields associated with said generating of saidmagnetic flux field, which fields would otherwise reach said targetarea.
 5. A magnetic coupling device, comprising: a coil having a firstside and a second side; a magnetic field pattern former; and themagnetic field pattern former covering the first side of the coil and atleast a portion of the second side of the coil.
 6. The magnetic couplingdevice of claim 5, wherein the coil is formed as at least a first traceon a printed circuit board.
 7. The magnetic coupling device of claim 5,wherein the magnetic field pattern former has a magnetic permeability ofat least
 20. 8. The magnetic coupling device of claim 5, wherein themagnetic field pattern former is ferrite.
 9. The magnetic couplingdevice of claim 8, wherein the ferrite is flexible and the ferrite isapplied to cover the first side of the coil, around at least a firstedge and at least a portion of a second side of the coil.
 10. Themagnetic coupling device of claim 9, wherein the portion of the secondside of the coil that is covered by the ferrite is at least 30 percent.11. The magnetic coupling device of claim 5, further including a firstRF shield covering a first side of the coil.
 12. The magnetic couplingdevice of claim 11, wherein the first RF shield has a loop shape with anopen circuit.
 13. The magnetic coupling device of claim 11, wherein thefirst RF shield is coupled to an electrical ground.
 14. The magneticcoupling device of claim 11, further including a second RF shieldcovering a second side of the coil.
 15. The magnetic coupling device ofclaim 6, further including a first RF shield covering the first trace;the first RF shield formed as a second trace on the printed circuitboard.
 16. The magnetic coupling device of claim 5, further including:at least one capacitor in one of series with the coil for seriesresonance and across the coil for parallel resonance.
 17. A planar coilprinted circuit board magnetic coupling device, comprising: a firsttrace on the printed circuit board forming the planar coil; a first RFshield, the first RF shield insulated from and covering a first side ofthe first trace; a second RF shield, the second RF shield insulated fromand covering a second side of the first trace; and a magnetic fieldpattern former covering a first side of the printed circuit board areacovered by the first trace and at least a portion of a second side ofthe printed circuit board area covered by the first trace.
 18. Themagnetic coupling device of claim 17, wherein: the first RF shield is asecond trace on the printed circuit board.
 19. The magnetic couplingdevice of claim 17, wherein: the first RF shield has an open circuit.20. The magnetic coupling device of claim 17, wherein: the magneticfield pattern former has a magnetic permeability of at least
 20. 21. Themagnetic coupling device of claim 20, wherein: the magnetic fieldpattern former is flexible ferrite.
 22. A method for increasing planarselectivity of a magnetic coupling device, comprising the steps of:covering an area of the magnetic coupling device where a magnetic fieldemanation is not desired with a magnetic field pattern former.
 23. Themethod of claim 22, wherein the magnetic field pattern former has amagnetic permeability of at least
 20. 24. The method of claim 22,wherein the magnetic field pattern former is flexible ferrite.
 25. Themethod of claim 24, wherein the flexible ferrite is arranged to cover afirst side of the magnetic coupling device, a first edge of the magneticcoupling device and at least a portion of a second side of the magneticcoupling device.
 26. A transponder communication selective module,comprising: a magnetic coupling device partially covered by a magneticfield pattern former; located proximate a media feed path; the mediafeed path arranged to carry a plurality of transponders sequentiallypast the magnetic coupling device.
 27. The apparatus of claim 26,further including a printhead arranged to apply indicia upon an outersurface of the transponders.
 28. The apparatus of claim 26, wherein theouter surface is a label.
 29. The apparatus of claim 26 wherein, themagnetic coupling device is formed as at least a first trace on aprinted circuit board.
 30. The apparatus of claim 26, wherein themagnetic field pattern former has a magnetic permeability of at least20.
 31. The apparatus of claim 26, wherein the magnetic field patternformer is ferrite.
 32. The apparatus of claim 31, wherein the ferrite isflexible and the ferrite is applied to cover the first side of themagnetic coupling device, around at least a first edge and at least aportion of a second side of the magnetic coupling device.
 33. Theapparatus of claim 32, wherein the portion of the second side of themagnetic coupling device that is covered by the ferrite is at least 30percent.
 34. The apparatus of claim 26, further including a first RFshield covering a first side of the magnetic coupling device.
 35. Theapparatus of claim 34, wherein the first RF shield has a loop shape withan open circuit.
 36. A system for sequentially communicating with aplurality of RFID transponders, comprising: a magnetic coupling devicelocated proximate a media supply path arranged to transport RFIDtransponders sequentially past the magnetic coupling device; themagnetic coupling device having a magnetic field pattern former arrangedto minimize magnetic flux emanation away from the magnetic couplingdevice, except through a gap; and the gap dimensioned to enableinductive coupling with only a single RFID transponder at a time.
 37. Amethod for selectively communicating with a desired RFID transponderamong a plurality of RFID transponders, comprising the steps of:energizing a magnetic coupling device; and passing the desired RFIDtransponder through a magnetic flux field generated by the magneticcoupling device; the magnetic coupling device covered on a first sideand at least a portion of a second side by a magnetic field patternformer whereby a magnetic flux field generated by the magnetic couplingdevice is in an area small enough so that only the desired RFIDtransponder is energized.
 38. The method of claim 37, wherein themagnetic field pattern former is formed from a flexible ferritematerial.